1. Field of the Invention
The present invention relates to a hybrid drive device, and in particular to a hybrid drive device mounted on a hybrid vehicle to improve the cooling performance for a winding wire of a stator.
2. Description of the Related Art
Generally, in conventional hybrid drive devices mounted on hybrid vehicles, a plurality of friction engagement elements, such as clutches and brakes, which are actuated by an engagement pressure supplied to a hydraulic servo are provided within the case of the hybrid drive device, and the transmission paths of the driving force from the internal combustion engine and from an electric motor are changed through a planetary gear unit according to the differential motion of the clutches and the brakes to transmit the driving forces to driving wheels located downstream while changing their rotational speeds and torques.
In general, the electric motor of a hybrid vehicle includes a stator having a wire wound around the outer periphery of a core fixed to a case, and a rotor provided at the inner peripheral part of the stator for free rotation. Because a large current flows through the wire, the temperature of the stator increases and the torque of the motor is reduced, the stator and the rotor need to be cooled.
Japanese Patent Application Publication No. 8-318741 (JP-A-08-318741), for example, discloses a hybrid vehicle in which a rotor is formed with a cylinder and a hydraulic actuator that supplies and discharges oil is provided in the cylinder. Oil discharged from an oil pump to cooling the rotor is introduced into the cylinder by the hydraulic actuator, and the oil is then supplied to the rotor by the hydraulic actuator, to cool the rotor and the stator.
Of the friction engagement elements described above, a brake provided in the planetary gear unit includes a plurality of separator plates attached to the inner peripheral part of a case, and a plurality of friction plates provided to the outer peripheral part of a ring gear and interposed between the separator plates. In this brake, when the separator plates are pressed by a hydraulic cylinder, the separator plates and the friction plates are engaged with each other. This engagement makes the ring gear stationary relative to the case, which changes the transmission path of the driving force.
In order to prevent of the friction plates and the separator plates from seizing up, Japanese Patent Application Publication No. 2007-1444 (JP-A-2007-1444) discloses a drive device in which the friction plates and the separator plates are supplied with oil for cooling.
In the drive device in which oil is supplied to the brake for cooling described in JP-A-2007-1444, oil is supplied from an oil pump to a supply hole formed in a rotary shaft of the planetary gear unit in the axial direction. The oil is then supplied to radial holes formed in a sun gear and a pinion gear of the planetary gear unit through radial holes formed in the rotary shaft and radially penetrating the supply hole, and then to the friction plates and the separator plates located on the outer peripheral part of the ring gear utilizing a centrifugal force due to rotation of the planetary gear unit.
In the hybrid drive device, however, the electric motor and the planetary gear that includes the friction engagement elements are housed separately from each other, with a partition wall interposed therebetween, in the case of the hybrid drive device, in order to support a bearing for the rotor and form a cylinder chamber in the brake. Therefore, two systems of oil supply paths are required to supply oil from the oil pump to both the electric motor and the friction engagement element, which necessitates the use of an oil pump having increased capacity.
In particular, because the winding wire which becomes hot is located on the outer side of the rotor in radial directions, a high-pressure oil pump must be used to supply oil from the hydraulic actuator provided in the rotor to the winding wire. Thus, the need to drive the high-capacity oil pump by the internal combustion engine may reduce the fuel efficiency of the vehicle.